Voltmeter



Dec. 3, 1946. P. D. zoTrU 2,412,191

VOLTMETER Filed' March 31, 1944 4 sheets-sheet 1 F@ 2 Bydvuwwav Dec. v3, 1946.

I P. D. zoT'rU voLTMETER Filed March 31, 1944 4 Sheets-Sheet 2 INVENTOR. 207-70.

Patented bec. 3, 1946 UNITED STATES PATENT OFFICE VOLTMETER Paul D. Zottu, Indian Hills, Ky., assigner to The Girdler Corporation, Louisville, Ky., a corporation oi Delaware Application March 3l, wat, Serial No. 528,34@

6 Claims.

L This invention relates to measuring instruments, more particularly to the measurement or" voltages at high frequency, and has for an ohject the provision oi1 a wide-range voltzneter of (Ci. lili-m95) in the output circuit of the rectifier is calibrated in terms of the line voltage or the voltage to be measured. Hence, if the meter reads 500, the voltage measured will be either 590 or a xed a simple, rugged construction and accurate 5 multiple thereof depending upon the setting of throughout the Wide range of voltages which it the spherical conductor. is capable ci measuring. For a more detailed explanation of the inven- In the development of high-frequency systems tion and for further objects and advantages for application to manufacturing processes there thereof, reference is to be had to the following has been need for a relatively simple means of lo description, taken in conjunction with the acmeasuring the voltages developed in the circuits. comparu/ing drawings in which: It has long been recognized that electrical energy Fig. l is a wiring diagram, diagrammatically at high frequency produces diathermy or inillustrating the relation oi the parts and their ternal heating of a wide variety of materials. associated circuits; These materials may vary from poor conductors l5 Fig. 2 is a fractional side elevation of the high to dielectrics or materials generally considered voltage capacitor; as non-conductors. For such a wide variety of Fig. 3 is a sectional View taken on the line 3-3 applications, the voltage and frequency of the of Fig. 5; output circuit are adjusted to best suit a partio- Fic". d is a sectional view taken on the line 4 4 ular application. 2li of Fig. 2;

ln accordance with the present invention, a FS. 5 is a fractional sectional elevation taken wide range voitineter is provided, which is rel on the line ae-5 of Fig. i; a'tively accurate over a range of from 500 to Fil?. 6 diag'ammlicly illustrates a mdied jlo volts or more. From the circuit to be form of theinventlon; v tested, a voltage is applied to two seriesconnect- 25 Fig. 7 is a plan view of an iris disc shown in Fig. ed capacitors, one of which is adjustable between t; and predetermined calibrated positions. For high Fig. 8 is a plan View oi a second iris disc havvoltages the adjustable capacitor preferably coning a smaller opening. sfmts ci an enlarged conductor forming one plate Referring to the drawings, a system embodyof the capacitor' and a fiat conductor forming 30 ing the invention will first be described, followed the other plate oi the capacitor. The flat plate by a more detailed description oi the structural upoorted from a metallic housinsy having an features or the multiplying capacitor. In the lng above the :'iat plate. The enlarged or system or" Fig. l, the invention is shown as com- .ierical conductor is movable aient a path nora pricing va high-voltage high-frequency vltmter to the fiat plate and to the opening in the 35 for the measurement of the voltage V appearing using. By increasing the spacing or air gap across the terminals ill and li. This voltage di herr/veen the spherical conductor and the iiat vides across two capacitors l2 and lil, connect conductor, the voltmeter is set for operation to ed in series between terminals i@ and il. Both measure voltages between differing limits. This capacitors are adjustable. For a given setting adjustment forms la multiplier for the voltmeter. 4o the capacity of the capacitor i3 is usually much For low voltages, the distance between the' larger than that of the capacitor l2. ln consespherical conductor and the at conductor is quence, the voltage across the capacitor i3 is usrelatively short. while for a voltage near the ually smaller than the voltage across the capacimaximum which is to be measured the distance tor l2 for the reason that the-voltage divides is substantial. The second capacitor may be i5 across the capacitors inversely with their calarge in comparison with the one including the pacitance. By making the capacitoritl very Spherical conductor. large in comparison with the capacitor li?, the inasmuch as the voltage divides across the voltages applied to the measuring circuit may not capacitors inversely with their capacitance, only only be of a reasonable order of magnitude, but a fraction of the voltage to be measured appears 50 entirely safe from an equipment and personnel across the larger capacitor. The fractional voltstandpoint. age which appears across the larger capacitor is The voltage appearing across the capacitor i3 applied to a rectiying device which produces an is applied by conductors it and it to a rectifyoutput current proportional to the applied high ing` device, preferably a diode lf3. The retid frequency voltage. A current meter connected 55 output from the diode is applied to a suitable in aaiaiai dicating device, such, for example, as a milliammeter I1, having a scale preferably calibrated in volts. By means of the network comprising the series-connected resistors I8, I9, and 2|, and the capacitor 22,- a substantially constant load is provided for the radiofrequency voltage which appears across the capacitor I3. The milliammeter I1 is connected in series with the resistor 2| which is variable or adjustable in order to provide an initial setting for the voltmeter which will read full-scale value for some convenient voltage across or between conductors I4 and I5. By means of a normally open sensitivity switch 25, the resistors I9, 20 and 2| may be removed or bypassed from the circuit of the milliammeter I1. While the removal of these resistors greatly increases the reading and sensitivity of the meter I1 the load across the capacitor I3 remains substantially constant. This result is accomplished by the circuit including resistor I 8 and the capacitor 22 whose reactance is relatively low as compared with the impedance offered by the resistors I9, 20 and 2| to the radiofrequency current. Hence, the inclusion or exclusion of the resistors I9-2I from the circuit does not materially change the load across the capacitor I3.

to the measurement f the output voltage of a high frequency oscillator or generator. During the starting up of such an oscillator, the load is to be gradually applied. Suitable adjustments of the circuit constants must be made to produce maximum output voltage. The problem is to determine whether a given change in capacitance or lnductance is in the right direction to increase the output voltage. Small changes in the circuit constants frequently produce small changes in the output voltage. These may not be of suiiicient magnitude to produce positive deflectiony ofv In terms of operation, the operator can then ascertain with certainty the effect of changing 'Ihe diode I6 is provided with a filament transformer 21 whose primaryv is connected to a suitable source of alternating current supply 29. The midpoint ofthe secondary winding is connected by conductor to the indirectly heated cathode of the diode I6. 'I'he direct.,.current circuit .for the meter I1, previously referred to, may be traced from the indirectly heated cathode by way of conductor I4, the meter I1, conductor 32, variable resistor 2|, the resistors I9g'fand 20 connected in parallel with each other, the resistor I8 and by conductor I5 to the anode of the diode I6.

The initial calibration of the voltmeter-is relatively simple. With the spherical conductor comprising the upper high voltage plate or electrode of capacitor I2 in a position of approximately maximum spacing from a iiat conductor forming the other plate or electrode of the capacitor I2, the maximum voltage for which the meter is designed is applied. Thus, for a live inch spacing between the electrodes 35 and 40, a voltage of 50,000 volts may be appliedbetween terminals I0 and II. 'I'he frequency may be of any value within wide limits, for example, from some thousands of cycles per second to a hundred million cycles or more per second. With the aforesaid voltage of 50,000 (peak) volts lat a frequency of say one million cycles per second, the capacitor I3 is adjusted until the pointer of meter I1' is deflected to its maximum or full-scale position. This may be accomplished by an R. F.

voltage of the order of 100 volts across the capacitor I3. The capacitor I3 and the resistor 2| are now locked in vtheir adjusted positions.

For all other voltage'ranges, the capacitor I2 is adjusted by moving spherical conductor 35 to predetermined positions. Thus it is in effect a multiplier and fixes the range of voltages for the meter I1. If the meter is calibrated in volts from 0 to 500, then for the highest range the multiplying factor may be 100. By decreasing the spacing between the capacitor electrodes 35 and 40 by predetermined increments, other multiplying factors in steps of III, from 1 to 100, may be provided. Once calibrated, the voltmeter as a whole continues effective as a satisfactorily accurate measuring device.

The importance of the sensitivity feature will be apparent by assuming the voltmeter is applied the tuning, the circuit constants or other variables of the high frequency oscillator as it is brought up to full load operation. It may be observed again that operation of the sensitivity switch 25A does not materially change the load across the capacitor I3 since that load is largely established by the resistor I8 and the series capacitor 22,k

whose reactance is relatively low as compared with the impedance offered by the resistors I 9-2I.

Coming now to the structural features characterlzing the invention, the capacitor I2 comprises the conductor or electrode 35 supported by a metallic stem 36 which is held in any desired position by means of a split-ring clamping device 31 provided with a clamping screw 38. The stem 36 as shown in Fig. 5 may be made of tubing with the lower end plugged, and threaded for threaded engagement with the electrode 35. As shown, the electrode 35 is spherical in shape and though this is the preferred construction, the invention is not limited thereto since other shapes may be used. For the higher voltages the electrode 35 should be provided with smooth or rounded edges to prevent corona discharge.

The cooperating capacitor electrode or plate t0 is shown in Fig. 3 to be circular although it can be of any desired configuration. Preferably it is supported, Figs. 2 and 5, below the upper wall dla. of a metallic housing 4I by means of an insulating supporting bar M. This bar is carried between adjusting nuts at the ends of threaded screws t5- and 36 which extend downwardly through the upper wall or cover plate Bla of housing 5I. The iiat circular electrode 40 is fastened to the bar 44 by means of a threaded screw d1 and'cooperating nut. The plate d0 is countersunk so that the head of screw 'lis flush with the upper surface thereof.

Just above the electrode 40 the central portion of the housing @la is cut away to provide opening 43, shown as circular and of somewhat less diameter than that of the electrode 40. This opening is closed by means of an insulating closure member 68, held in place by means of additional nuts on the screws 45 and 46.

The movable electrode 35 is supported from the upper plate ila of housing il by means of three insulators 50, 5I and 52, which may oe of aclarar 7 trode with respect' to said first electrode thereby to change the voltage range of the device.

2. The combination, with a high-voltage measuring device in which a rectied current varies in accordance with the voltage to be measured, of a metal plate having an opening extending through the mid-portion thereof, a capacitor including at least a first electrode and a second electrode, electrical insulating means for supporting said i-lrst'electrode in spaced relation with said opening and concentrically thereof, a plurality of insulating supports secured to said plate and extending outwardly therefrom, means including a clamping device carried by the outer ends of said insulating members, said second electrode including a supporting stem adapted to be held by said clamping device, whereby' said lastnamed electrode may be supported in different predetermined positions with respect to said first electrode.

3. In a high-voltage high-frequency measuring device in which a vrectified current varies in accordance with the voltage to be measured, the combination of a pair of series-connected capacitors across which the voltage divides inversely with respect to their capacities, a circuitconnected vacross the larger of said capacities and including a rectifying device for producing said rectified current, a network connected in parallel with said larger capacitor for producing a substantially constant load across said larger capacitor, said network including a resistor and a third capacitor connected in series with veach other and in shunt across said large capacitor, said network also including at least one additional resistor, and means for increasing the magnitude of said rectified current Without asubstantially changing the load across said larger capacitor comprising a switch for removing said last-named resistor from said circuit.

4. The combination, with a high-voltage highfrequency measuring device in which a rectified current varies in accordance with the voltage to be measured, of a. high-voltage capacitor which comprises electrodes relatively movable to diier- Y ent positions with respect to each other to change 4 frequency measuring device of the type in which a rectified current varies in accordance with the voltage to be measured, of a series-circuit including two capacitors one of which is relatively large with respect to the other, said smaller capacitor being characterized by the provision of two electrodes one of which is movable relative tothe other. means including one of said electrodes for applying to said series-circuit the voltage to be measured, means for holding one `of said electrodes in dierent predetermined positions with respect to the other to predetermine the capacity therebetween and thereby iix the voltage range of the measuring device, and adjusting shielding means interposed between said electrodes for predetermining the proportion of the electric eld which may then exist between said electrodes further to change the voltage range of the measuring device.

6. The combination, with a high-voltage measuring device in which a rectied current varies in accordance with the voltage to be measured, of a metal plate having an opening extending through the mid-portion thereof, a capacitor including at least a first electrode and a second electrode, electrical insulating means for supporting said first electrode in spaced relation with said opening, a plurality of insulating supports secured to said plate and extending outwardly therefrom, means including a .clamping device carried by the outer ends of said insulating members, said second electrode including a supporting stern adapted to be held by said clamping device, whereby said lastnamed electrode may be supported in different predetermined positions with respect to said first electrode.

PAUL D. ZOTTU. 

